Crossword clue: difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge

The most common answer is abstruse (8 letters).

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

Possible answers

abstruse 8 letters wn-def

difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge

recondite 9 letters wn-def

difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge